MRI is an imaging method which magnetically excites nuclear spin of an object placed in a static magnetic field with an RF pulse having the Larmor frequency and reconstructs an image based on MR signals generated due to the excitation. The above-mentioned MRI means magnetic resonance imaging, the RF pulse means a radio frequency pulse, and the MR signal means a nuclear magnetic resonance signal.
Here, an RF coil device is a device which transmits an RF pulse to nuclear spin inside an object by, for example, supplying a coil with an RF pulse electric current and receives generated MR signals.
The RF coil devices are classified into three types: a type exclusively for transmitting RF pulses, a type exclusively for receiving MR signals, and a dual-purpose type which performs both transmission of RF pulses and reception of MR signals. In addition, the RF coil devices are classified into a whole body type and a local type.
Because MR signals emitted from an object are weak and it is preferable to receive the MR signals at a position as close to the object as possible, various types of local RF coil devices in terms of shape are used in accordance with an imaging anatomical part. For example, in the case of imaging of a shoulder joint, a dedicated RF coil device for the shoulder joint is attached to the shoulder of an object.
In many cases, the whole body type RF coil device is included in a gantry of an MRI apparatus, as the dual-purpose type of performing transmission of RF pulses and reception of MR signals. Since a local RF coil device is directly attached to a patient, a local RF coil device is exposed to mechanical vibration due to attachment and detachment, vibration due to insertion and extraction of its connector into/from a connection port of an MRI apparatus, and large electric power of radio frequency inside the gantry. Because local RF coil devices are used under more severe conditions compared with each control component of an MRI apparatus as explained above, a failure of a local RF coil device may occur frequently.
Although a failure of a local RF coil device can be detected to some degree when it is connected to an MRI apparatus and used, a failure of a local RF coil device is not immediately detected in many cases. For example, a failure of a local RF coil device may occur when it is detached from an object after completion of imaging, or it may also occur while it is stored. If a local RF coil device having a failure is attached to a patient, and if the failure is detected after start of imaging, not only imaging of the object cannot be performed but also a large amount of cost and time is wasted. In order to avoid such waste of time and cost, it is desirable that failure of an RF coil device should be detected as early as possible.